1. Field of Invention
This invention relates to barium titanate based dielectric compositions, and more particularly to barium titanate based dielectric compositions having relatively small proportions of guest ions such as zirconium, manganese, molybdenum, magnesium, yttrium, silicon, and additional barium dispersed within the barium titanate crystal matrix. Such a dielectric composition can be used to form multilayer ceramic chip capacitors having internal base metal electrodes formed of nickel or nickel alloys.
2. Description of Related Art
Multilayer ceramic chip capacitors have been widely utilized as miniature-sized, high capacitance, and high reliability electronic components. In accordance with increasing demands for high-performance electronic equipment, multilayer ceramic chip capacitors also have encountered marketplace demand for smaller size, higher capacitance, lower cost, and higher reliability.
Multilayer ceramic chip capacitors generally are fabricated by forming alternating layers of an internal electrode forming paste and a dielectric layer-forming paste. Such layers are typically formed by sheeting, printing, or similar techniques, followed by concurrent firing.
Generally, the internal electrodes have been formed of conductors such as silver, gold, palladium, platinum, (i.e., “noble metals”) or alloys of the foregoing. Although noble metals are expensive, they can be partially replaced by the use of relatively inexpensive base metals such as nickel or copper and their alloys. A “base metal” as used herein is any metal other than silver, gold, palladium, and platinum. Base metal internal electrodes can become oxidized if fired in ambient air, so the dielectric layers and base metal internal electrode layers must be co-fired in a reducing atmosphere. Firing in a reducing atmosphere, however, causes the dielectric layers to be reduced, which decreases resistivity. Multilayer ceramic chip capacitors using non-reducible dielectric materials have been proposed, however, such devices typically have a shorter life of insulation resistance (IR) and low reliability.
The Electronic Industry Association (EIA) prescribes a standard for the temperature coefficient of capacitance (TCC) known as the X8R characteristic. The X8R characteristic requires that the change of capacitance be no greater than ±15% with respect to the reference temperature of 25° C. over the temperature range −55° C. to +150° C. X8R components exhibit capacitance aging no greater than 2.5% per decade.